A standard power actuator for a chuck, mandrel, or like machine tool adapted to hold a tool or a workpiece that is being machined typically has a hollow cylinder housing generally centered on an axis and normally fixed to, for instance, the chuck body, and a piston axially displaceable but nonrotatable in the housing, defining therein a pair of axially opposite pressurizable compartments, and normally fixed, for instance, to the jaw-actuating member of the chuck. A piston stem centered on the axis, fixed to the piston, and extending axially from the piston is formed with a pair of separate feed passages each having one end opening into a respective compartment and an opposite end opening axially on the stem. A distributor body rotatable about the axis on the stem at the opposite ends of the passages is provided with respective connections communicating with the opposite ends, so that the compartments can be pressurized via the respective passages and connections for axial movement of the piston and stem in the housing, thereby moving the jaws on the chuck body. Structure on the stem and body permits the body to rotate about the axis thereon but prevents the body from moving axially on the stem.
In order to use such an actuator in an automated machining system it is necessary to provide a position-monitoring unit that itself is connected to a controller that in turn operates the valves that themselves control the actuator. This is typically done by providing on the cylinder housing a bearing that is connected to an outrigger that carries a switch- or sensor-actuating member that can coact with a switch or sensor carried on the distributor body that itself is fixed axially but not rotationally on the piston stem. Thus this actuating member is axially but not rotationally fixed on the cylinder housing so that as the cylinder housing and piston move axially relative to each other the actuating member will move past the switch/sensor. The relative positions of the switch/sensor and the actuating member can be set such that, for instance, the switch/sensor is actuated when the chuck is fully opened or closed.
In German patent document No. 3,117,850 the outrigger is a flat slide which runs in guide grooves formed in the distributor body. The flat slide has its front end fixed on a split ring which is mounted via a bearing on the cylinder housing. The split ring has a pair of shoulders which axially oppositely engage this bearing, clamping this ring in place on the outer race of the bearing.
Such an arrangement is expensive with regard to the formation of the rod and of the guide for the outrigger, and requires that the outrigger ring fit perfectly on the bearing. Furthermore the radial spacing of the guides for the outrigger must be very accurately machined, thereby making manufacture of the system quite costly.
This German patent document also discloses an arrangement wherein the cylinder housing is provided with an element forming a radially outwardly open guide groove in which a roller on the outrigger engages. In such an arrangement there are considerable frictional losses. In addition there is inherently some axial play between the roller and the guide groove because without such play the roller would certainly jam. This play clearly results in somewhat inaccurate response from the sensor/switches.